Electron discharge device



Jan; 28,1941. M. HARNISCH ELECTRON DISCHARGE DEVICE Filed May 27, 1938 INVENTOR. MARTIN HARNISCH ATTORNEY.

Patented Jan. 28, 1941 UNITED STATES EN OFFICE 2,229,738 ELECTRON DISCHARGE DEVICE Martin Harnisch, Berlin-Siemensstadt, Germany,

assignor to Siemens and Halske Aktiengesellschaft, Siemensstadt-Berlin, Germany, a corpo- I ration of Germany Application May 27, 1938, Serial N 0. 210,292

In Germany June 15, 1937 1 Claim.

carrying capacity of a tube may be increased by increasing the heat dissipated by the plate. In the art of building screen-grid tubes the suggestion has been made to make the anodes in the form of sheets or plates placed in a radial position. The heat dissipated by the anodes will then not be held in the electrode space. It is radiated 01f freely in all directions. With tubes of this kind, with the same constructional size, essentially larger powers may be handled than, for instance, with the electrode systems or assemblies known in the prior art in which the anodes are cylindrical.

Now, it would be desirable to equip power triodes also of the kind here concerned, with such plate-shaped radial anodes. However, any such plan is attended with the following practical difficulties. In the design of power triodes, there exists generally the requirement that the inner resistance of the tube be as low as may be possible, for this is desirable for the full control or swing of the plate currents from zero to satu- 80 ration Without dissipation. Now, the inner resistance may be reduced in two ways: (1) the characteristic slope is made steep, or (2) the grid transparency (or mutual controllance) is made high, that is the amplication factor a is 88} made small. For a given cathode, a steep slope (mutual conductance) means small distance between grid and cathode. However, this means a greater possibility of a varying amplification factor; hence, certain limitations are imposed. If

401a low inner resistance is to be secured, there is often the necessity of raising the grid transparency (131.), that is reducing the amplification factor. However, in the case ,of systems with radial anode-plates the amplification factor is high, and it would be hard to reduce it by moving the anode-plates to a position closer to the control grid lest lack of symmetry arise in the amplification factor. Hence, other ways and means must be found for decreasing the am- 50 plification factor so as to make it possible to leave the anode-plates at a certain distance from the control grid.

One of the principal objects of this invention is to provide an improved electron discharge 55 device particularly suitable for power purposes.

According to the invention, between plate. and control grid an additional or auxiliary grid is mounted, this grid being in conducting relationship with the anode. The position of this grid with reference to the control grid proper will then govern the'size or value of the amplification factor, while the anode elements of sheet metal or the plate parts are proportioned only from the viewpoint of load-carrying capacity. It I will be understood that the auxiliary grid connected to the anode absorbs also part of the lessened still further by disposing the wires of l the auxiliary grid in an appropriate manner, that is by aligning the control and auxiliary grids so that'they will lie in the shadow of the wires of the control grid. I

The arrangement of the invention makes it feasible to choose for the anode or plate any desired form at all, in other words, to design the anode so as to insure optimum conditions for dissipating .and removing the heat generated at the anodes, but without an incidental production of appreciable distortion of the amplification factor. For instance, the sheets making up the anode or plate may be mounted staggered, shifted or twisted with reference to the rest of the electrode system or assembly rather than mounting them perfectly symmetrically.

Another merit of the auxiliary grid as here disclosed resides in the fact that in certain applications of the idea, for instance, in transmitter tubes in what is called overloaded operation, such secondary electrons as may be released from the plate elements will be unable to reach the control grid for the reason that over this path or trajectory from the plate elements to the auxiliary grid, they encounter no accelerating potential. The auxiliary grid, as will be seen, is always at the same potential (both D. C. and A. C.) as the very plate or anode which carries the major part of the load.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claim, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figures 1 to 4 inclusive show transverse sections of various electrode arrangements of iliary grid 3.

electron discharge devices made according to this invention.

Referring to Figure 1, a. cathode I either of the direct or the indirectly heated kind is surrounded by a control grid 2 supported by the side rods 9 and I0. Disposed around the control grid is the auxiliary or supplemental grid 3 which is secured on the supports 1 and 8. The distance between the auxiliary grid 3 and the control grid 2 is of importance so far as the value of the grid transparency and hence the amplification factor is concerned, since the auxiliary grid is in conducting relation with the rectangular anode sheets or elements 4 and 5 so that it represents an advanced portion of the anode or plate. Secondary electrons which would be most likely to arise first about the marginal portions, for instance, of the anode 4, in order to have a chance to reach the control grid would have to travel along the edge 6 of the anode as far as the aux- However, on this trajectory, because of the fact that the potential of the two electrodes 3 and 4 and 5 is the same, they fail to find any boosting or accelerative field, and the result is that they do not reach the space confined or enclosed by the auxiliary grid.

Figure 2 shows the electrode system or assembly comprising three anode sheets or plate members l4, l5, l6 staggered on angle of degrees in reference to one another. Also in this case there is a cathode H, being, for instance, of the indirectly heated type, a control grid l2 and an auxiliary grid l3 connected to the anode elements.

The present invention is advantageously usable also for flat cathodes as shown in Figure 3. The flat indirectly heated cathode I1 is surrounded by the control grid IS, the two being matched as to shape. l9 designates the auxiliary grid, and 20, 2| indicate the plateor sheet-shaped anode members.

Figure 4 shows a similar embodiment, however, with this, distinctive feature that the cathode 22 is of the directly heated kind and that the same consists of a plurality of filamentary wires placed zigzag fashion in one plane. 23 denotes the control grid, 24 is the auxiliary or supplemental grid, and 25, 26 the two plate sheets.

As can be easily seen from the drawing, the heat dissipated by the sheets composing the anode or plate elements is able to unobstructedly reach the ambient space. In fact, only a minor portion of the heat will strike the auxiliary grid; hence, it will not be able or liable to give rise to undesired electronic emission any more than the control grid. The auxiliary grid itself is heated by the current which it absorbs only to a limited degree since this current is small; indeed, in cases where no special steps are adopted to counteract this efiect it will hardly exceed one-fifth of the total plate current. However, by the arrangement before described for the positioning of the wires of the auxiliary grid in the shadow of the control-grid wires, or by similar and equivalent measures, the temperature of the said grid may be kept inside acceptable limits.

While I have indicated the preferred embodiments of my invention of which I am now aware An electron discharge device having a cathode and a pair of concentric grids surrounding said cathode, the grid wires of said grids being aligned, and a plurality of radially positioned anode ele ments positioned outside of said grids and electrically connected to the grid adjacent the anode elements.

MARTIN HARNISCI-I. 

